1. Field of the Invention
The present invention relates to an apparatus for manufacturing a sheet such as a ceramic green sheet.
2. Description of the Related Art
Ceramic green sheets have been conventionally used for manufacturing monolithic ceramic capacitors and multi-layer ceramic substrates. Since the miniaturization of electronic devices has been advancing, such ceramic green sheets are required to be thinner accordingly. However, thinner ceramic green sheets become mechanically weaker and more fragile. Therefore, flexible carrier films are prepared, on which ceramic green sheets are formed. According to this method, a ceramic green sheet backed with a carrier film can be obtained.
Japanese Unexamined Patent Application Publication No. 11-77627 discloses a conventional apparatus for manufacturing a ceramic green sheet using a carrier film, comprising a means for transferring a carrier film, an applying means for applying ceramic slurry onto the carrier film, and a drying means, such as a drying oven, for drying the ceramic slurry on the carrier film to form a sheet.
In the conventional ceramic green sheet-manufacturing apparatus, in order to control the green sheet thickness, the following process is generally used. The thickness of a dried sheet is measured. Then, a measurement of the thickness is fed back to the ceramic slurry-applying means, whereby the coating thickness of the ceramic slurry applied onto the carrier film is adjusted. However, in this process, the feedback is delayed and the thickness cannot be efficiently controlled.
On the other hand, it has been proposed to measure the coating thickness of the ceramic slurry applied onto the carrier film in a wet mode before drying, by use of a special optical measuring instrument. In this technique, however, the final thickness of the sheet that will exist after drying must be precisely estimated, from the coating thickness of the wet ceramic slurry at the time of its measurement. If the estimation is not precise, the thickness cannot be precisely controlled.